1. Field of the Invention
The present invention relates to an optical member driving apparatus, an optical pickup apparatus including the optical member driving apparatus, and an optical disc apparatus including the optical pickup apparatus.
2. Description of the Related Art
There are introduced commercially large-capacity optical discs supporting a blue-violet laser beam/LASER (Light Amplification by Stimulated Emission of Radiation) such as a “Blu-ray Disc” (registered trademark) and an “HD DVD” (registered trademark) (High Definition DVD). As compared with the conventional optical discs such as a CD (Compact Disc) (registered trademark) and a DVD (registered trademark) (Digital Versatile Disc), the large-capacity optical discs such as the “Blu-ray Disc” and “HD DVD” have a remarkable feature, for example, that a high-density and multilayer technique has substantially been established and the high-densification and multilayer technique has been further improved.
Literature describing the multilayer discs includes, for example, a Japanese Patent Application Laid-Open Publication describing a large capacity optical disc that enables high-speed and stable recording, reproducing, and erasing of signals: without reducing storage capacity of the disc; and with reducing time for recording signals into a RAM unit for recording signals; and with eliminating the possibility of entrance of dust, etc., between layers of the RAM unit and a ROM unit (see, e.g., Japanese Patent Application Laid-Open Publication No. Hei9-180257 (p. 4 and FIGS. 1 to 10)).
“RAM” is the abbreviation of “Random Access Memory”. “ROM” is the abbreviation of “Read Only Memory”.
When a laser beam is applied to a multilayer optical disc, spherical aberration occurs to the laser beam spot formed by irradiation on a signal layer of the optical disc due to difference in thickness of a cover layer making up the optical disc, for example. “Aberration” means that a light beam having passed through a lens, for example is not correctly focused so that an incomplete image is formed. For example, the “spherical aberration” means a phenomenon that a light beam is not able to be focused on the optical axis.
literature describing a measure against the spherical aberration includes, for example, a Japanese Patent Application Laid-Open Publication describing an optical disc recording and reproducing method with which the spherical aberration due to the difference in thickness of the cover layer can be corrected even during recording of a recordable optical disc having one or a plurality of recording layers, and which an operation is not required for obtaining an optimum position to correct the spherical aberration every time an optical disc is mounted (see, e.g., Japanese Patent Application Laid-Open Publication No. 2006-302420 (pp. 1 and 3, and FIGS. 1 to 6)).
A common spherical aberration correction mechanism in an optical head apparatus, i.e., an optical pickup apparatus, includes a mechanism for driving a collimator lens, which converts a laser beam into a parallel light, a diffused light, or a convergent light, by using a motor such as a DC motor, for example.
Literature introducing the mechanism for driving a collimator lens using a motor such as a DC motor includes, for example, a Japanese Patent Application Laid-Open Publication describing: an optical head and a recording and/or reproducing apparatus capable of suppressing spherical aberration even if numerical aperture NA (Numerical Aperture) is increased; a recording and/or reproducing method capable of suppressing spherical aberration even if the numerical aperture NA is increased; and a thickness detection method capable of easily detecting the thickness of an optical transmission layer of an information recording medium having the optical transmission layer formed on its recording layer (see, e.g., Japanese Patent Application Laid-Open Publication No. Hei11-259906 (pp. 3 and 15, and FIGS. 12 and 13)).
A “numerical aperture” refers to the product of: a sine of an angle obtained when the effective radius of an objective lens (radius of entrance pupil) of an optical device, for example, is viewed from an object point; and refractive index of a medium on the incident side. A numerical aperture is used when describing performance of an objective lens, for example.
Some problems have been imposed on an optical pickup apparatus so that the optical pickup apparatus correctly and promptly correspond to a multilayer optical disc. One of the outstanding problems is, for example, how promptly the spherical aberration is corrected by an optical pickup apparatus, which aberration is generated between layers of an optical disc due to incorporation of multiple layers into the disc, when a laser beam is applied to a signal layer of the multilayer optical disc.
For example, in the case where a laser beam is applied to a signal layer of an optical disc by using an optical pickup apparatus including a motor and a collimator lens, when the motor is used to drive the collimator lens, vibration is always transmitted from the motor to the collimator lens during the operation of the motor. For example, even if a stop signal is sent to stop the motor, the collimator lens continues to vibrate and then stops after a small time lag, due to the influence of the vibration, etc., transmitted from the motor to the collimator lens. A problem has arisen that the optical pickup apparatus can stably read a signal recorded in the signal layer of the optical disc only after the collimator lens stops, i.e., a time period of, for example, about several tens msec (milliseconds) to 50 msec has elapsed, for example.
Concerns are rising that in the case where there is some wait until the collimator lens stops still, for example, when a multilayer optical disc is mounted in an optical disc apparatus including an optical pickup apparatus and a speedy game is being played with the apparatus, waiting time is often necessary while the game being played, so that it is difficult to play the speedy game smoothly.
For example, when a multilayer optical disc having software of a speedy game recorded thereon is mounted in an optical disc apparatus including an optical pickup apparatus and the game is played, there is frequently executed inter-layer jumping of the beam spot of a laser beam emitted from the optical pickup apparatus for signal layers of the optical disc. To support this, a necessity has arisen for a more speedup of aberration correction of the beam spot by the optical pickup apparatus for signal layers of the optical disc.
In order to increase the speed of the aberration correction of the beam spot of the optical pickup apparatus for signal layers of the multilayer optical disc, when the inter-layer jumping is frequently executed of the beam spot of the laser beam emitted from the optical pickup apparatus to signal layers of a multilayer optical disc, a proposal has been made that the collimator lens is driven at a higher speed by driving the motor at a higher speed, for example.
However, the fact is that, even if the collimator lens is driven at a high speed by driving the motor at a high speed, a certain waiting time is necessary until the vibration of the collimator lens caused by the vibration transmitted from the motor is reduced after the motor has stopped. As a result, the speedup of the aberration correction by the optical pickup apparatus for the multilayer optical disc is not realized.
When the collimator lens is forcibly driven at a high speed by forcibly driving the motor at a high speed, an irregular sound is generated while the collimator lens is being driven. It is also worried that a problem may arise to the durability of the optical pickup apparatus including driving members such as the motor and optical members such as the collimator lens due to high-speed driving of the motor, collimator lens, etc.
An optical member driving apparatus is desirable that includes an aberration correcting mechanism capable of promptly executing the aberration correction of the laser beam spot formed by irradiation on each signal layer of the multilayer optical disc even if the inter-layer jumping of the beam spot is frequently executed for signal layers of the optical disc, and an optical pickup apparatus including such an optical member driving apparatus is also desirable. An optical member driving apparatus with both of improved durability and improved reliability, and an optical pickup apparatus including the optical member driving apparatus with both of improved durability and improved reliability are also desirable.